全文获取类型
收费全文 | 566249篇 |
免费 | 66719篇 |
国内免费 | 45807篇 |
专业分类
电工技术 | 51482篇 |
技术理论 | 8篇 |
综合类 | 61984篇 |
化学工业 | 69748篇 |
金属工艺 | 39719篇 |
机械仪表 | 40904篇 |
建筑科学 | 44350篇 |
矿业工程 | 24785篇 |
能源动力 | 14868篇 |
轻工业 | 58429篇 |
水利工程 | 19389篇 |
石油天然气 | 20572篇 |
武器工业 | 9327篇 |
无线电 | 59665篇 |
一般工业技术 | 46668篇 |
冶金工业 | 22074篇 |
原子能技术 | 9202篇 |
自动化技术 | 85601篇 |
出版年
2024年 | 2319篇 |
2023年 | 8824篇 |
2022年 | 22038篇 |
2021年 | 28302篇 |
2020年 | 20461篇 |
2019年 | 14226篇 |
2018年 | 15376篇 |
2017年 | 17433篇 |
2016年 | 15702篇 |
2015年 | 25350篇 |
2014年 | 32166篇 |
2013年 | 37573篇 |
2012年 | 47850篇 |
2011年 | 50021篇 |
2010年 | 47553篇 |
2009年 | 45084篇 |
2008年 | 46583篇 |
2007年 | 45323篇 |
2006年 | 38831篇 |
2005年 | 31670篇 |
2004年 | 22577篇 |
2003年 | 14786篇 |
2002年 | 13741篇 |
2001年 | 12452篇 |
2000年 | 9911篇 |
1999年 | 4048篇 |
1998年 | 1506篇 |
1997年 | 1159篇 |
1996年 | 1043篇 |
1995年 | 813篇 |
1994年 | 612篇 |
1993年 | 572篇 |
1992年 | 498篇 |
1991年 | 293篇 |
1990年 | 292篇 |
1989年 | 307篇 |
1988年 | 212篇 |
1987年 | 136篇 |
1986年 | 126篇 |
1985年 | 77篇 |
1984年 | 80篇 |
1983年 | 70篇 |
1982年 | 61篇 |
1981年 | 97篇 |
1980年 | 173篇 |
1979年 | 112篇 |
1976年 | 14篇 |
1965年 | 17篇 |
1959年 | 111篇 |
1951年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Qiqi Peng Xu Jiang Yifan Chen Wei Zhang Jun Jiang Anquan Jiang 《Ceramics International》2021,47(16):22753-22759
Large domain wall (DW) conductivity in an insulating ferroelectric plays an important role in the future nanosensors and nonvolatile memories. However, the wall current was usually too small to drive high-speed memory circuits and other agile nanodevices requiring high output-powers. Here, a large domain-wall current of 67.8 μA in a high on/off ratio of ~4460 was observed in an epitaxial Au/BiFeO3/SrRuO3 thin-film capacitor with the minimized oxygen vacancy concentration. The studies from read current-write voltage hysteresis loops and piezo-response force microscope images consistently showed remaining of partially unswitched domains after application of an opposite poling voltage that increased domain wall density and wall current greatly. A theoretical model was proposed to explain the large wall current. According to this model, the domain reversal occurs with the appearance of head-to-head and tail-to-tail 180° domain walls (DWs), resulting in the formation of highly conductive wall paths. As the applied voltage increased, the domain-wall number increased to enhance the on-state current, in agreement with the measurements of current-voltage curves. This work paves a way to modulate DW currents within epitaxial Au/BiFeO3/SrRuO3 thin-film capacitors through the optimization of both oxygen vacancy and domain wall densities to achieve large output powers of modern domain-wall nanodevices. 相似文献
44.
Jiangyou Long Qingfa Peng Gaopan Chen Yuliang Zhang Xiaozhu Xie Guoshun Pan Xiaofeng Wang 《Ceramics International》2021,47(16):23134-23143
Femtosecond (fs) lasers have been proved to be reliable tools for high-precision and high-quality micromachining of ceramic materials. Nevertheless, fs laser processing using a single-mode beam with a Gaussian intensity distribution is difficult to obtain large-area flat and uniform processed surfaces. In this study, we utilize a customized diffractive optical element (DOE) to redistribute the laser pulse energy from Gaussian to square-shaped Flat-Top profile to realize centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates. We systematically investigated the effects of processing parameters on the changes in surface morphology and composition, and an optimal processing strategy was provided. Mechanisms of the formation of surface nanoparticles and the removal of surface micro-burrs were discussed. We also examined the distribution of subsurface defects caused by fs laser processing by removing a thin surface layer with a certain depth through chemical mechanical polishing (CMP). Our results show that laser-induced periodic surface structures (LIPSSs) covered by fine SiO2 nanoparticles form on the fs laser-processed areas. Under optimal parameters, the redeposition of SiO2 nanoparticles can be minimized, and the surface roughness Sa of processed areas reaches 120 ± 8 nm after the removal of a 10 μm thick surface layer. After the laser processing, micro-burrs on original surfaces are effectively removed, and thus the average profile roughness Rz of 2 mm long surface profiles decreases from 920 ± 120 nm to 286 ± 90 nm. No visible micro-pits can be found after removing ~1 μm thick surface layer from the laser-processed substrates. 相似文献
45.
46.
全膜电容器边缘处的电场畸变是影响电容器元件击穿的重要因素之一.为研究浸渍情况和压紧系数对全膜电容器电场分布的影响,对电容器端部进行建模,通过改变浸渍情况和压紧系数,计算不同参数下电容器端部的电场分布情况,结果表明:未浸渍情况下电场最大值集中在折边处两侧,浸渍情况下场强在折边圆弧处分布较为均匀.同时发现,在浸渍情况下增大压紧系数K可以明显改善全膜电容器端部电场的分布情况. 相似文献
47.
48.
Peng Li Haibin Jiang Ariel Barr Zhichu Ren Rui Gao Hua Wang Weiwei Fan Meifang Zhu Guiyin Xu Ju Li 《Advanced functional materials》2021,31(51):2105845
Mercury, lead, and cadmium are among the most toxic and carcinogenic heavy metal ions (HMIs), posing serious threats to the sustainability of aquatic ecosystems and public health. There is an urgent need to remove these ions from water by a cheap but green process. Traditional methods have insufficient removal efficiency and reusability. Structurally robust, large surface-area adsorbents functionalized with high-selectivity affinity to HMIs are attractive filter materials. Here, an adsorbent prepared by vulcanization of polyacrylonitrile (PAN), a nitrogen-rich polymer, is reported, giving rise to PAN-S nanoparticles with cyclic π-conjugated backbone and electronic conductivity. PAN-S can be coated on ultra-robust melamine (ML) foam by simple dipping and drying. In agreement with hard/soft acid/base theory, N- and S-containing soft Lewis bases have strong binding to Hg2+, Pb2+, Cu2+, and Cd2+, with extraordinary capture efficiency and performance stability. Furthermore, the used filters, when collected and electrochemically biased in a recycling bath, can release the HMIs into the bath and electrodeposit on the counter-electrode as metallic Hg0, Pb0, Cu0, and Cd0, and the PAN-S@ML filter can then be reused at least 6 times as new. The electronically conductive PAN-S@ML filter can be fabricated cheaply and holds promise for scale-up applications. 相似文献
49.
Jinming Wang Meng Yang Guodong Zou Di Liu Qiuming Peng 《Advanced functional materials》2021,31(21):2101180
Lithium (Li) metal, as an appealing candidate for the next-generation of high-energy-density batteries, is plagued by its safety issue mainly caused by uncontrolled dendrite growth and infinite volume expansion. Developing new materials that can improve the performance of Li-metal anode is one of the urgent tasks. Herein, a new MXene derivative containing pure rutile TiO2 and N-doped carbon prepared by heat-treating MXene under a mixing gas, exhibiting high chemical activity in molten Li, is reported. The lithiation MXene derivative with a hybrid of LiTiO2-Li3N-C and Li offers outstanding electrochemical properties. The symmetrical cell assembling lithiation MXene derivative hybrid anode exhibits an ultra-long cycle lifespan of 2000 h with an overpotential of ≈30 mV at 1 mA cm−2, which overwhelms Li-based anodes reported so far. Additionally, long-term operations of 34, 350, and 500 h at 10 mA cm−2 can be achieved in symmetrical cells at temperatures of −10, 25, and 50 °C, respectively. Both experimental tests and density functional theory calculations confirm that the LiTiO2-Li3N-C skeleton serves as a promising host for Li infusion by alleviating volume variation. Simultaneously, the superlithiophilic interphase of Li3N guides Li deposition along the LiTiO2-Li3N-C skeleton to avoid dendrite growth. 相似文献
50.
新型建筑工业化具有高质量、低消耗、可循环发展等特征,其推广已上升到国家战略层面。利用演化博弈方法,建立“政府-开发商-银行” 的三方动态演化博弈模型,进行各博弈主体策略的演化稳定性分析,并针对初始状态、奖惩力度、借贷风险和开发成本等对演化结果的影响进行动态仿真。在此基础上, 考虑开发商群体的网络拓扑特征对演化真实性的影响,引入复杂网络理论, 以无标度网络为载体描述开发商个体的连接偏好和决策机制,构建政府监管下的建筑工业化扩散模型,并通过仿真深入研究相关因素对扩散深度的影响作用,最后结合仿真结果给出相应对策建议。 相似文献